Bone cement compositions comprising fused fibrous compounds

ABSTRACT

The preferred embodiment of the present invention provides novel and unique fused fibrous compounds for addition to and manufacture of bone and dental cement systems and methods of making the same. The preferred embodiment of the fused fibrous compound material made therefrom comprises a rigid three-dimensional network of fibers fused together at their points of contact wherein said network is greater than 60% by volume void space, has mean pore diameters greater than 10 microns, or both. The fused fibrous compound is preferably manufactured from fibers and a fusion source and is added to the composition in particle form.

FIELD OF THE INVENTION

[0001] This application is a continuation of U.S. application Ser. No.10/470,702 filed Apr. 4, 2003, now U.S. Pat. No. 6,752,863, which is acontinuation of U.S. application Ser. No. 09/952,770 filed on Sep. 14,2001, now U.S. Pat. No. 6,544,324, which is a continuation patentapplication of U.S. patent application Ser. No. 09/174,753, filed Oct.19, 1998, now U.S. Pat. No. 6,291,547, which is a continuation of U.S.patent application Ser. No. 08/684,251, filed on Jul. 19, 1996, nowabandoned, which was a continuation-in-part of U.S. patent applicationSer. No. 08/386,305, filed Feb. 8, 1995, now issued as U.S. Pat. No.5,621,035.

[0002] The invention is directed to improved bone cement and dentalcement systems comprising fused fibrous compounds and methods of makingthe same. The invention is further directed to bone cement and dentalcement system kits for bone or teeth repair or other treatment of boneand teeth.

BACKGROUND OF THE INVENTION

[0003] In joint surgery it is common practice today to anchor componentsof replacement joints by using as bone cement a two-component resinwhich polymerizes during the operation at normal temperatures and which,on account of its plastic properties leads to an interlocking of theprosthesis component in the bony sheath. Because of its physicalproperties, the bone cement shrinks onto the prosthesis resulting in aclosed metal-to-cement contact.

[0004] The bone cements commonly used are polymethylmethacrylate (PMMA)consisting of powdery bead polymers which are superficially dissolved byliquid monomers and embedded during the polymerization process. Duringmixing the polymer is immersed in the monomers. The PMMA beads aresuperficially dissolved and embedded in a composite manner. Despitetheir widespread use PMMA and related bone cements tend to represent the“weak link” in prosthesis fixation.

[0005] The long term success of a total joint prosthesis depends on thecontinued function and interaction of each of the components of theprosthetic system. In a cemented total hip prosthesis, for instance,stress transfer from the pelvis to the femur is a function of thematerials between the two bones (e.g. bone-PMMA-metal-Ultra-highMolecular Weight Polyethylene-metal-PMMA-bone) and the interfacesbetween the materials. The weakest of the materials is the PMMA, withthe lowest fracture toughness and ultimate strength.

[0006] The common mode of failure of total joint prostheses is asepticloosening. X-ray examinations of patients with loosened prostheses oftenreveal a radiolucent line in the bulk of the cement, indicating that thecement has fractured. Because the geometry of the prosthesis is complex,the state of stress is also highly complex, and the reasons for cementfailure are not clear. For example, it has been postulated that theintegrity of the metal stem/PMMA interface is the critical link in theperformance of the prosthesis; however, the cause and effectrelationship between the metal prosthesis/PMMA interface failure andcement fracture is not well understood although the fracture mechanicsof the two phenomena are most likely linked. The improvement of thefracture characteristics of the bone cement, however, is a problem thathas received some attention in recent years.

[0007] The composition of the PMMA used for total joint surgeries todayis substantially the same as that used 20 years ago; very little hasbeen done to improve the material itself. The acceptable success rate ofcemented prostheses was achieved using existing cements, however, in apredominantly elderly patient population and with improved surgicalhandling techniques. The 90% success rate at ten years is good, butshould be improved. Cement failures do occur, and generally lead torevision surgery. Furthermore, younger patients now receiving totaljoint replacements have a greater life expectancy than the designexpectations of the total joint prosthesis. Improvement of the bonecement, exclusively, may not solve every problem associated with totaljoint replacements. But, by making improvements in each component of atotal joint prosthesis, including the cement, the success rate ofprostheses will improve, and mechanical failures can be virtuallyeliminated.

[0008] Increasing the longevity of PMMA by improving the resistance tofailure of the polymer has received some, albeit surprisingly little,attention in the bioengineering literature in the past ten years. Onesuggested method of improvement was to formulate a new bone cement,based on n-butyl methacrylate, rather than the methyl methacrylatemonomer. It has been reported that the material showed a higherductility, a higher apparent fracture toughness, and a greater fatiguelife. However, the actual fracture toughness determined by separateimpact tests showed no improvement of the new cement with respect toPMMA cements. An even more detrimental result was that the new polymerhad only half the modulus and half the ultimate tensile strength ofPMMA.

[0009] Another method of attempting to improve PMMA was the addition ofa reinforcing phase, generally short fibers or whiskers. Early work wasdone by Knoell, et al., Ann. Biomed, Eng., 3, 1975, pp. 225-229 withcarbon fibers approximately 6 mm in length, 1, 2, 3 and 10% fibercontent by weight (approximately 0.67, 1.33, 1.96 and 5.87% fibercontent by volume, with measured increases of 100% in the averageYoung's modulus for the reinforced PMMA. They also reported a decreasein peak curing temperature of the reinforced PMMA. They found thereinforced cement viscous and difficult to mix, and they altered theratio of powder polymer to liquid monomer to facilitate mixing of thereinforced cement. Pilliar, et al., J. Biomed. Mater. Res., Vol. 10,1976, pp. 893-906); Fatigue of Filamentary Component Materials ASTM STP636, eds. Reifsnider, et al., ASTM 1977, pp. 206-227; used carbon fibers(6 mm length, 7 micrometers diameter) with a 2% volume content. Theymeasured a 50% improvement in tension-tension fatigue limit, improvedimpact performance, and a 36% increase in ultimate tensile strength.However, it was implied that the reinforced PMMA had poor intrusioncharacteristics due to increased viscosity, and poor fiber distribution.Wright, et al. J Mater Sci. Let., 14 1979, pp. 503-505, did preliminarystudies using PMMA reinforced with chopped aramid fibers. PMMAreinforced with 5.17% by volume (7% by weight) exhibited a 74% increasein fracture toughness over the plain PMMA. They were not able to producereinforced PMMA with a fiber content greater than 5% by volume becauseof mixing and handling difficulties. Beaumont, J. Mater. Sci., 12, 1977,pp. 1845-1852 included glass beads in the PMMA mass and measured a 10³decrease in crack propagation velocity, using 30% volume content of thebeads.

[0010] Very few investigations involved the use of metal fibers toreinforce PMMA. Taitsman and Saha, J. Bone Joint Surg., Vol. 59-A, No.3, Apr. 1977, pp. 419-425, used large diameter (0.5 to 1.0 mm) stainlesssteel and vitallium wires as a reinforcing phase. They embedded 1, 2, or3 wires in their PMMA specimens. They reported up to an 80% increase intensile strength of the PMMA, with three embedded vitallium wires, butnoted that clinical applications of their wire reinforced cement werelimited. Taitsman and Saha's use of reinforcing wires is analogous toreinforcing bars embedded in structural concrete, and not a homogeneous,fiber composite material. Fishbane and Pond, Clin. Orthop., No. 128,1977, pp. 194-199, reinforced industrial grade PMMA and PMMA bone cementwith stainless steel whiskers (0.5-1.0 mm length and 65 micron diameter;3-6 mm length and 90 microns diameter). They determined that theaddition of fibers up to 6.5% by volume improved the compressivestrength by nearly 100% for the industrial PMMA, but only 25% for thesurgical grade PMMA. The compressive strength of PMMA is not a criticalproperty for the longevity of the cement in vivo. These authorspostulate that the reason for the decreased performance of the surgicalPMMA was: “ . . . due to the limitations imposed by the (surgical)methacrylate preparation technique.”

[0011] Schnur and Lee, J. Biomed. Mater Res., Vol. 17, 1983, pp.973-991, used titanium (Ti) sheet, wire, mesh and powder as areinforcing phase with the purpose of increasing the modulus of PMMA tothe modulus of cortical bone. A 16% volume fraction of 1 mm diameterwires (a total of 25 wires) increased the modulus of the PMMA by 380%,and the maximum compressive stress by 75%. The concept is again similarto the reinforcing bars embedded in concrete.

[0012] The more recent work in reinforcing PMMA bone cement as reportedin the literature, has involved either carbon, graphite, or aramidfibers. Robinson, et al., J. Biomed. Mater. Res., Vol. 15, 1981, pp.203-205, tested both regular PMMA and low viscosity PMMA cement(available from Zimmer Co., Warsaw, Ind.) reinforced with 2% volume ofcarbon fibers (1.5 mm in length, 10 microns diameter). Both reinforcedcements exhibited an increase in apparent fracture toughness (notchedbending strength tests) of approximately 32% over their plaincounterparts. Surface fractography revealed no evidence of fiberfracture, indicating that the increases in “toughness” was dueprincipally to fiber pull out. In other work with carbon fiberreinforced PMMA an order of magnitude decrease in crack propagationvelocity was attributed to the carbon fiber reinforcement of both theregular and low viscosity cements.

[0013] Saha and Pal, J. Biomechanics, Vol. 17, No. 7, 1984, pp. 467-478,tested PMMA reinforced with carbon fibers, 0.67% by volume (1% byweight; 6 mm length, 8 microns diameter) and PMMA reinforced with aramidfibers (Dupont Kevlar-29), 1.61 and 3.82% by volume (2 and 4% by weight;12-13 mm length, unspecified diameter). The reinforced PMMA showed anincrease in the ultimate compressive strength of 20.5% for the carbonfibers, and 19.5% and 28.7% for the 1.61 and 3.82% volume % aramidfibers, respectively. Two important consequences of the addition offibers to PMMA were proposed: The peak temperature of the reinforcedPMMA was lower than the plain PMMA, and the addition of fibers changedthe workability of the cement. They recognized that uniform dispersionof fibers was not achieved. Saha and Pal studied a machine mixingtechnique for distributing the fibers. Their claim that machine mixedspecimens were stronger than non-machine mixed specimens is misleading.They used a different shaped fiber for their machine mixed specimens. Itis the superior shape of the fiber which is presumed to account for theincrease in strength. Machine mixing was never shown to improve theproperties of reinforced PMMA.

[0014] Ekstrand, J. Biomed. Mater. Res., Vol. 21, 1987, pp. 1065-1080,fabricated carbon fiber reinforced PMMA by using clinically irrelevant,industrial fabrication techniques with fiber content as high as 16.38%by volume (40% by weight).

[0015] Recent work by Pourdeyhimi, et al., Ann. Biomed. Eng., 14, 1986,pp. 277-294, studied the effect of the fiber content of the fracturetoughness of hand-mixed, reinforced, dental PMMA. They used aramidfibers from 0.82 to 5.17% by volume (1 to 7% by weight), and graphitefrom 0.67 to 5.87% by volume (1 to 10% by weight). For each type offiber reinforced cement, the fracture toughness increased with increasedfiber content. The aramid fiber specimens showed a greater increase thanthe carbon fiber specimens of the same weight percent, presumablybecause the energy dissipated in the micromechanisms of failure isgreater for the aramid fibers than for the carbon fibers. They were notable to produce a uniform distribution of the fibers.

[0016] U.S. Pat. No. 4,064,566 to Fletcher, et al. discloses a graphitefiber reinforced bone cement of the acrylic type stated to havemechanical properties more nearly matched to those of bone and thermalcuring characteristics resulting in a lower exothermic temperaturereaction during curing. The bone cement composition is a dispersion offrom 2 to 12% by weight of very fine high modulus graphite fibers havinga diameter below 50 microns and between 0.1 and 15 mm in average lengthin a solution of biocompatible polymer dissolved in a reactive monomer.Fletcher reports only an increase in the modulus of the bone cement,which may not be of primary concern to a reinforced bone cement, andindeed can be detrimental to the prosthesis system. There was a decreasein compressive strength, and more negatively, a decrease in flexuralstrength for the reported composite.

[0017] U.S. Pat. No. 4,239,113 to Gross, et al. discloses an acrylicbased bone cement filled with between 15 and 75% by weight of inorganicmaterial comprised of about 90 to 99% by weight of a bio-active glassceramic powder and about 1 to 10% by weight of vitreous mineral, e.g.,glass, fibers having a length below about 20 mm. The particle size ofthe powder is from 10 to 200 micrometers. Fiber diameters are notdisclosed. Improvements in impact strength, and compression strengthwere reported. However, a significant decrease in the bending strengthand an increase in the modulus of elasticity were also reported.Further, there are no examples given as to the clinical usefulness ofthis cement. Bioactive glass degrades with time, and hence the integrityof the reinforced bone cement will also degrade with time. Thecontrolled experimentation shows that there is no mechanical improvementdue to the fiber reinforcing phase alone. Any improvement is due to thecombination of bioactive glass and fiber in concert. Since the bioactiveglass degrades with time, the properties of the reinforced cementproposed by Gross, et al. will also degrade with time.

[0018] Davidson, in U.S. Pat. No. 4,735,625, reports the invention of areinforced bone cement formed using a sock-like mesh of a fiber-likematerial to reinforce the cement in the vicinity of the prosthesis. Thevolume of “reinforced” bone cement is limited; critical areas are notreinforced. Draenert, in U.S. Pat. No. 4,365,357, presents an inventionsimilar to Davidson's, but using a mesh of polymeric fibers. Theinvention is restricted to use in repairing bone defects, and not as abone cement in the sense described for total joint arthroplasty.Draenert, in U.S. Pat. No. 4,718,910, describes a bone cement mixturewhere a second phase of fibers is added. The fibers, however, are madeup of the same polymeric material as the bone cement. Draenert includesa graph of the performance of the new material versus existing cements.The inventor states that the fiber is only effective because of theshape of the prepolymer powder. Therefore, the improvement is due to theuse of a different cement, and not to the addition of the fibers.

[0019] Ducheyne et al. in U.S. Pat. No. 4,963,151 disclose thedistribution of short, fine, reinforcing fibers homogeneously throughoutsurgical bone cement by adding the fibers in the form of bundles ofseveral hundred fibers with the fibers bonded to each other with anadhesive binder that is soluble in the liquid monomer component of thebone cement.

[0020] It is generally agreed that as the quantity of reinforcing fibersincreases so do the mechanical strength properties. However, as thefiber content increases it becomes increasingly difficult and eventuallynot practical or possible to effect homogeneous distribution of thefibers throughout the cement mass and in addition the viscosity of themass increases and its workability by the surgeon during surgerydecreases. Any practically useful surgical bone cement must be capableof being easily mixed by the surgeon in a clinical setting, i.e., duringsurgery, and must remain sufficiently flowable and workable to beapplied to the bone surface or cavity and/or to the prosthesis or otherimplant device.

SUMMARY OF THE INVENTION

[0021] Accordingly, it is an object of the invention to provide asurgical bone dental cement with improved mechanical properties,including fracture toughness and fatigue strength, thereby improvinglong term prognosis of total joint replacements and other surgical bonerepair treatments involving bone cements.

[0022] It is another object of the invention to provide a fused fibrousreinforced surgical bone dental cement wherein mixing of the fiberreinforcement into the cement matrix can be easily performed by thesurgeon under clinical conditions.

[0023] Still other objects of the invention are to provide a novel fusedfibrous reinforcing material which can be easily and homogeneouslyincorporated into a two component bone or tooth cement includingbiocompatible polymer beads or powder and biocompatible reactive liquidmonomers; a bone dental cement treatment kit for surgical bone/toothrepair which kit includes the fused fibrous material, biocompatiblepolymer and reactive liquid monomer; and a method for uniformly andhomogeneously incorporating fused fibrous material into a two componentacrylic based surgical bone/dental cement.

[0024] The above and other objects of the invention which will becomemore apparent after reading the following detailed description andpreferred embodiments in conjunction with the accompanying drawings areaccomplished, according to a first aspect of the invention, by anacrylic based surgical bone cement with fused fibrous compound addedthereto.

[0025] The fused fiber material can be provided as a component of a boneor tooth cement treatment kit for surgical bone/dental repair or othertreatment of a bone/dental disease or bone/dental defect requiringapplication of a surgical bone/dental cement. The kit includes abiocompatible polymer, generally in the form of powder or beads, aliquid reactive monomer, and a plurality of fused fibrous compoundparticles wherein the fibers in each particle are fused to each other attheir points of contact with a fusion source, said fusion point notsoluble in the liquid reactive monomer.

[0026] The present invention, according to one embodiment, is directedto an improved bone cement composition comprising bone/dental cement,and a fused fibrous compound. According to another embodiment, thebone/dental cement composition may comprise polymethylmethacrylate,methylmethacrylate-styrene-copolymer, and a radiopacifier. According tofurther embodiment, the bone cement composition comprises bariumsulfate.

[0027] According to some embodiments, the bone/dental cementcompositions of the present invention may include fused fibrouscompounds in the form of particles of different sizes, e.g., rangingfrom about 10 microns to about 1000 microns in diameter.

[0028] According to further embodiments, the bone/tooth cementcompositions of the present invention may be comprised of fused fibrouscompound of up to about 10%, 20%, 30%, 40%, 50%, 60% and/or 70% of thetotal weight of the composition.

[0029] According to another embodiment, the bone cement compositions ofthe present invention may comprise fused fibrous compounds having atleast about 60% by volume void space and/or mean pore diameters ofgreater than about 10 microns. Preferably, the compound of the presentinvention comprises 88% by volume void space. Probably, the bone/teethcement compositions of the present invention include fused fibrouscompounds which are silanated.

[0030] According to a still further embodiment of the present invention,the bone/dental cement compositions of the present invention may includefused fibrous compounds manufactured from alumina fibers, silica fibersand a fusion source, e.g., boron nitride. Preferably, the bone/dentalcement compositions of the present invention include fused fibrouscompounds comprising about 21% by weight alumina and about 74% by weightof the fused fibrous compound. Preferably, the bone/dental cementcompositions of the present invention include fused fibrous compoundsmade from alumina fibers having an average diameter of from about 1 toabout 100 microns and silica fibers having an average diameter of fromabout 1 to about 6 microns.

[0031] The present invention is also, according to a further embodiment,directed to methods for improving bone/dental cement compositionscomprising adding fused fibrous compounds (e.g., those described above)to bone/dental cement compositions.

[0032] A bone/dental cement treatment kit for bone repair or othertreatment of a bone/dental defect, said kit comprising: (1) finelydivided acrylic polymer, (2) polymerizable liquid acrylic monomers forpreparation of bone/dental cement useful in bone/tooth repair or otherbone/tooth treatment, and (3) a fused fibrous compound.

BRIEF DESCRIPTION OF THE FIGURES

[0033]FIG. 1 is a plot or graph of the density versus the porosity ofthe fused fibrous compound of the present invention.

[0034]FIG. 2 is a bar graph illustrating the flexural strength ofvarious bone cement compositions reinforced with the fused fibrouscompound of the present invention.

[0035]FIG. 3 is a bar graph illustrating the flexural modulus of variousbone cement compositions reinforced with the fused fibrous compound ofthe present invention.

[0036]FIG. 4 is a bar graph illustrating the linear shrinkage of bonecement reinforced with the fused fibrous compound of the presentinvention.

[0037]FIG. 5 is a plot illustrating the polymerization temperatureversus the time after polymerization initiation of various bone cementcompositions reinforced with the fused fibrous compound of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] In this invention, the terms “(meth)acrylate” and“poly(meth)acrylate” include the monomers and polymers, respectively, ofmethacrylic acid esters and acrylic acid esters, and the polymers alsoinclude the co-polymers of the compounds named.

[0039] The preferred bone cement material to which the fused fibrouscompound is added includes a solid finely divided powdery or granularpolymer component and a liquid reactive or polymerizable monomercomponent which is also a solvent or swelling agent for the polymercomponent. The polymer and monomer components can be based on theacrylic, e.g., (meth)acrylate system, however, other polymeric systemscan also be used. For convenience, the cement system may at times bebroadly referred to as an acrylic polymer, or as based on PMMA(polymethylmethacrylate), the preferred polymer component. While theinvention is described herein in terms of a preferred embodiment, i.e.,bone cement, it is to be understood that the invention is also directedto dental/tooth cements.

[0040] More generally, the polymer component of the composition can beany methyl(meth)acrylate polymer such as methyl(meth)acrylatehomopolymers and copolymers of methyl(meth)acrylate with alpha,beta-ethylenically unsaturated compounds such as vinyl acetate, alkyl(e.g., C₂-C₆) (meth)acrylates and multi-functional acrylic monomers suchas alkylene dimethacrylate and alkylene diacrylates and triacrylates.These polymers generally have a molecular weight between 500,000 and2,000,000. Methylmethacrylate homopolymers and copolymers are preferred.

[0041] The reactive monomer component is preferably methyl acrylate ormethyl methacrylate although the C₂-C₄ alkyl(meth)acrylates, such asethyl(meth)acrylate, propyl(meth)acrylate or (n-, oriso-)butyl(meth)acrylate, can also be used. These bone cement materials,which are themselves well known and commercially available, are usuallyprovided with 2 parts by weight of the finely divided polymer and 1 partby weight of liquid monomer, although higher or lower ratios can also beused, and are characterized as being self-polymerizable substances whichare mixed, together with a polymerization catalyst, such as dibenzoylperoxide, and polymerization accelerator, such as dimethyl-p-toluidine,immediately prior to the operation to form a viscous liquid or pastymass. The pasty mass is introduced into the appropriate body cavityand/or to the surgical implant, device, and will harden in situ, at roomtemperature (via an exothermic reaction) within a few minutes.

[0042] More specifically, curing of bone cement composition is typicallyaccomplished by any suitable initiator system such as from about 0.1 toabout 3% by weight, preferably about 0.6% of a conventional free radicalinitiator. The initiator can be a peroxy compound or an azo compound.For purposes of biocompatability benzoyl peroxide is a very suitablefree radical initiator. The curing temperature is generally reduced toroom temperature, e.g. about 25° to 30° C., by inclusion in theformulation of an activator for the peroxide catalyst which causes morerapid decomposition of the peroxide to form free radicals. Suitableperoxide catalysts include benzoyl peroxide, 2,4-dichlorobenzoylperoxide and 4-chlorobenzoyl peroxide. Activators or accelerators forthese catalysts include N,N-dialkyl anilines or N,N-dialkyl toluidinesgenerally employed in amounts ranging from about 0.1 to 1% based on theweight of monomer present. A preferred activator isN,N-di(2-hydroxyethyl)-p-toluidine. In order to provide longer shelflife for the compositions of the invention, the composition may bestored in a closed container at cold temperature. Stabilizers, such ashydroquimone or chlorophyll may also be added to the monomer compound.Bone cements containing both activator and peroxide are provided astwo-part compositions in which the activator and monomer and peroxideand polymer component are packaged in separate containers. Theproportions by weight of polymer and liquid monomer can range from about4:1 to 1:2, preferably 3:1 to 1:1.5, such as 2:1, 1.5:1, 1:1 or 1:1.5.

[0043] Generally, the fused fibrous compound component of the presentinvention has been described above in the Summary Of The Invention.However, several fused fibrous compound compositions falling within thedescription set forth above are particularly preferred. Generally, thefused fibrous compound materials of the present invention aremanufactured utilizing alumina fibers, silica fibers, and from about 1%to about 5% boron, preferably boron nitride.

[0044] One preferred embodiment of the fused fibrous compound materialof the present invention is comprised or manufactured from of about 1%to about 50% by weight alumina, from about 50% by weight to about 98% byweight silica, and boron. Another preferred embodiment of the fusedfibrous compound material is manufactured utilizing: (1) from about 15%to about 30% by weight alumina fiber; (2) from about 65% to about 85% byweight silica fiber; (3) from about 1% to about 3% by weight siliconcarbide; and (4) from about 1% to about 5% by weight boron nitride.

[0045] Another more preferred fused fibrous compound material of thepresent invention is manufactured from: (1) about 21% by weight aluminafiber; (2) about 74% by weight silica fiber; (3) about 2% by weightsilicon carbide; and (4) about 2.85% by weight boron nitride.Preferably, the material of the present invention is manufacturedutilizing alumina and silica fibers in a ratio of 22:78 by weight. Forstrength, a preferred ratio of alumina to silica is 30:70 by weight.

[0046] Moreover, a preferred embodiment of the fused fibrous compoundmaterial of the present invention comprises: a rigid three-dimensionalnetwork of inorganic or organic fibers fused together at their points ofcontact wherein said network has mean pore diameters of greater thanabout 10 microns, or has greater than about 60% by volume void space, orboth. The fused fibrous compound may be, in some embodiments, in theform of particles or branched fibers.

[0047] The fused fibrous compound materials of the present inventionhave many advantageous properties needed for bone cement applications.The fused fibrous compound material of the present invention hasexceptional physical, chemical, and mechanical properties which areimparted to varying degrees depending upon the application to bonecements manufactured utilizing the material, these properties include,inter alia: (1) low to high density—4 lb./ft.³ to 62 lb./ft.³; (2) lowthermal conductivity—e.g., for 12 lb./ft.³ density at 500° F.conductivity=0.61 Btu-in./ft.²; (3) purity—predominately comprised of99.7% pure silica fibers and 95.2% pure alumina fibers; (4) long life incyclic applications—e.g., 12 lb./ft.³ density, does not degrade withcyclic exposure to 2600° F. and can even withstand limited exposure to2900° F.; (5) rigidity—maintains shape and supports mechanical loadswhile providing thermal insulation (i.e., has a high compressivestrength and tensile strength (MN/m2) (6) high flexural strength—modulusof rupture for 4 lb./ft.³ to 62 lb./ft.³ densities ranges from 100-6200lb./in.²; (7) inert—does not burn, softens at temperatures above 2700°F. and melts at about 3100° F.; (8) dimensional stability—has a lowcoefficient of thermal expansion and 0.4% linear shrinkage; (9) thermalshock resistance—can be heated to 2600° F. and immediately immersed incold water without damage; (10) high diffusivity—12 lb./ft.³ to 62lb./ft.³ ranges from 97% to 56%; (11) porosity—highly porous (over 60%by volume void space, preferably between about 60% and about 98% byvolume void space, most preferably over 80% by volume void space) andoffers minimal resistance to the passage of gases or liquids (mean porediameters greater than 10 microns, generally between 10 and 25 microns,most preferably from about 20 to about 22 microns); (12) able to coat orbond to other materials (i.e., materials, plastics, metals, inorganics)with relative ease to enhance characteristics. In addition, the 16lb/ft³ density filler material of the present invention has (1) aflexural modulus of strength—2.5×10¹⁰ Pa, (2) a Rockwell Hardness—50,(3) Surface Roughness of 0.6 Ra, and (4) linear shrinkage of 0.4% afterrepeated cycles at temperatures above 2700° F. As a result, e.g., thebone cements made with the fused fibrous compound material of thepresent invention have heretofore unknown improved linear shrinkage,flexural strength, and flexural modules.

[0048] Generally, the process for the manufacture of low density, like16 lb. per ft.³, fused fibrous compound material (discussed in terms ofa preferred alumina/silica embodiment) is comprised of the followingsteps:

[0049] (1) preparation of a slurry mixture comprised of pre-measuredamounts of purified fibers/materials and deionized water;

[0050] (2) removal of shot from slurry mixture;

[0051] (3) removal of water after thorough mixing to form a soft billet;

[0052] (4) addition of a ceramic binder after the formation of thebillet;

[0053] (5) placement of the billet in a drying microwave oven formoisture removal; and

[0054] (6) sintering the dry billet in a large furnace at about 1600° F.or above.

[0055] High purity silica fibers are first washed and dispersed inhydrochloric acid and/or deionized water or other solvents. The ratio ofwashing solution to fiber is between 30 to 150 parts liquid (pH 3 to 4)to 1 part fiber. Washing for 2 to 4 hours generally removes the surfacechemical contamination and non-fibrous material (shot) which contributesto silica fiber devitrification. After washing, the fibers are rinsed 3times at approximately the same liquid to fiber ratio for 10 to 15minutes with deionized water. The pH is then about 6. Excess water isdrained off leaving a ratio of 5 to 10 parts water to 1 part fiber.During this wash and all following procedures, great care must be takento avoid contaminating the silica fibers. The use of polyethylene orstainless steel utensils and deionized water aids in avoiding suchcontamination. The washing procedure has little effect on the bulkchemical composition of the fiber. Its major function is theconditioning and dispersing of the silica fibers.

[0056] The alumina fibers are prepared by dispersing them in deionizedwater. They can be dispersed by mixing 10 to 40 parts water with 1 partfiber in a V-blender for 2½ to 5 minutes. The time required is afunction of the fiber length and diameter. In general, the larger thefiber, the more time required.

[0057] Generally, in order to manufacture ultra-low density fusedfibrous ceramic filler material, for example, densities below 12lb./ft.³, the process includes the additional steps of:

[0058] (1) the addition of expendable carbon fibers in the castingprocess and/or other temporary support material; and

[0059] (2) firing the billet at about 1300° F. to remove the carbonfibers or other support material prior to the final firing atapproximately 1600° F. or above.

[0060] When the dispersed silica fibers and dispersed alumina fibers arecombined, the pH is probably acidic and should be adjusted to neutralwith ammonium hydroxide. The slurry should contain about 12 to about 25parts water to about 1 part fiber. The slurry is mixed to a uniformconsistency in a V-blender in 5 to 20 minutes. The boron nitride can beadded at this point (2.85% by weight of the fibers) and mixed to auniform consistency in a V-blender for an additional 5 to 15 minutescreating a Master Slurry. The preferred mixing procedure uses 15 partswater to 1 part fiber and the slurry is produced in about 20 minutes ofmixing. At lower density formulations, expendable carbon fibers are usedto give “green” strength to the billet prior to the final sintering. Thepercent of carbon fiber used varies greatly depending on the diameter,length and source of the fiber and the ultimate density of the materialbeing produced. The percent of carbon fiber per dry weight of materialshould range between 1 and 10%. The source of the carbon fiber can takemany forms including nylon, cellulose, and purified graphite basedcarbon in fibrous form. Carbon fibers added in the casting process areeliminated by firing the billets at 1350° F. prior to the final firingat 2450° F.

[0061] The Master Slurry is poured into a mold for pressing into thedesired shape. The water is withdrawn rapidly and the resulting felt iscompressed at 10 to 20 psi. Rapid removal of the water is required toprevent the fibers from separating. If graded properties are desired inthe resultant material, the slurry can be allowed to settle and thefibers to partially separate before the removal of the water.

[0062] The final density of the finished restorative material isdetermined in part by the amount of compression placed on the felt,varying the wet molded dimension in relation to the fiber content. Theformulation of the present invention has been prepared in densitiesranging from about 0.05 to 0.48 g/cc. It can, however, be prepared inlower and higher densities, e.g., ranging from 64 kg/mm³ to 1000 kg/mm³.

[0063] After molding, the restorative material is dried and fired by thefollowing preferred procedure. The material is first dried in an ovenfor 18 hours; the temperature, initially 38° C., is raised at a rate of11° C. per hour to 104° C., held there for 4 hours, raised again at arate of 1° C. per hour to 150° C., and held there for 4 hours. Thematerial is taken directly from the drying oven, placed in the firingfurnace, and fired. A temperature rise rate of 220° C. per hour or lessis required in order to avoid cracking and warping in the case of a 15cm×15 cm×7.5 cm block of material. For larger blocks, slower heatingrates may be required. The maximum firing temperature may vary from1200° C. to 1600° C. depending upon the fiber ratio used, amount ofboron nitride, and the final density of the material that is desired.

[0064] The temperature rise rate is chosen to permit relatively uniformtemperatures to be achieved throughout the material during the process.A faster temperature rise rate causes non-uniform temperatures to beachieved throughout the material during the process. A fastertemperature rise rate causes nonuniform strength and density and maycause cracking. Longer or higher temperature firing results in highershrinkage and related greater resistance to subsequent shrinkage, aswell as a shorter lifetime to devitrification under cyclic exposures tohigh temperatures. The maximum firing temperature is dependent upon thefiber ratio used and the density of the composite desired. The firingtime and maximum temperature are selected to allow sufficient shrinkageto achieve stabilization and fiber fusion while not allowing anydevitrification.

[0065] After firing, the material may be machined to obtain any desiredfinal dimensions. Only about 0.5 cm of the material must be machinedoff.

[0066] The procedure used to prepare the fused fibrous compound materialof the present invention, may be varied through a rather broad rangewith satisfactory results. In one variation, the silica fibers may beborated and prefired prior to use. This process is used to improve themorphological stability and physical properties of the resultantmaterial.

[0067] The following examples of fused fibrous compounds are provided toillustrate the invention by describing various embodiments, includingits best mode as presently conceived. All proportions used are expressedon a percent by weight basis unless otherwise noted.

EXAMPLE 1

[0068] An embodiment of the fused fibrous matrix ceramic material of thepresent invention having a density of 0.32 g/cc, and opacified withsilicon carbide was produced, with 825 grams of silica fibers, 175 gramsalumina fiber (average diameter—11 microns, length—0.32 cm), 35 grams1200 grit silicon carbide, 2.85 grams of boron nitride, 10 millilitershydrochloric acid, 5 milliliters ammonium hydroxide and deionized water.The silica fibers were washed as in Example 2.

[0069] The alumina fibers were placed in a 7,570 ml capacity stainlesssteel double shell blender with 5,000 grams deionized water and mixedusing an intensifier bar for 2½ minutes to disperse the fiber.

[0070] The washed silica fibers, dispersed alumina fibers, boronnitride, and silicon carbide were placed in a 28.31 liter stainlesssteel double shell V-blender. Deionized water was added to bring thetotal weight to 15,000 grams. The ammonium hydroxide (5 ml) was added toadjust the slurry to basic before mixing. The slurry was mixed,degassed, transferred to a mold and pressed into a billet as in Example2.

EXAMPLE 2

[0071] The materials used were the following: 150 grams aluminasilicatefibers (AS-32, manufactured by 3-M Company containing 80% Al₂O₃ and 20%SiO₂), 1000 grams of silica fibers (Microquartz 108), 35 grams of 1200grit silicon carbide, 30 grams of boron nitride, 10 ml of hydrochloricacid, 5 ml of ammonium hydroxide, and deionized water.

[0072] The silica fibers were placed in a polyethylene container in 32liters of deionized water. Hydrochloric acid (10 ml) was added to bringthe pH to 3. Pure nitrogen was bubbled through the mixture to agitatethe fiber and assist washing. Agitation was continued for two hours. Theacidic water was then drained off, fresh deionized water added and themixture again agitated with pure nitrogen for 15 minutes. The rinsingprocess was repeated 2 more times which brought the pH to about 6.0.

[0073] The aluminasilicate fibers were placed in a 7,570 ml capacitystainless steel double shell blender with 5,000 grams of deionized waterand mixed using the intensifier bar for 2½ minutes to disperse thefiber.

[0074] The washed silica fibers, dispersed aluminasilicate fibers, boronnitride, and silicon carbide were placed in a 28.31 liter stainlesssteel double shell V-blender. Deionized water was added to bring thetotal weight to 18,000 grams. Ammonium hydroxide (5 ml) was added toadjust the slurry to basic before mixing. The slurry was then mixed withthe intensifier bar running for 20 minutes, removed from the V-blenderand degassed, transferred into a mold, and pressed into a 21.6 cm×21.6cm×10 cm billet. The top and bottom of the mold were perforated andcovered with a 16 mesh aluminum screen to allow the excess water to flowout.

[0075] The billet was dried in an oven for 18 hours beginning at 38° C.,increased at 11° C. per hour to 104° C., held for four hours at 104° C.,increased at 11° C. per hour to 150° C. and held four hours at 150° C.After drying, the billet was transferred to the firing furnace. Thefurnace temperature was increased at a rate of 220° C. per hour to thefiring temperature, 1315° C., where it was held for 1½ hours. Afterfiring, the temperature was decreased at a rate of 220° C. per hour to980° C. where the furnace was turned off, then allowed to cool to roomtemperature.

[0076] The usefulness of boron oxide in the two-fiber composites of thisinvention is demonstrated by the following preparations.

EXAMPLE 3

[0077] In one run, an experimental mixture was made containing 25%aluminasilicate fibers (“FIBERFRAX H,” manufactured by the CarborundumCompany, containing 62% Al₂O₃ and 38% SiO₂) and 75% pure silica fibers(“MICROQUARTZ 108”). The mixture was ground with mortar and pestle andthen fired at 1400° C. for 5 hours. The resulting product underwent 48%devitrification. When the aluminasilicate fibers were prefired withboron oxide (85% and 15% respectively) at 1100° C. for 90 minutes andthen mixed with the silica fibers and fired as above, the productexhibited no devitrification.

EXAMPLE 4

[0078] An acceptable 17 cm×17 cm×7.5 cm billet of material having adensity of 0.11 g/cc was produced using 600 grams of silica fibers, 90grams of aluminaborosilicate fibers (average diameter—11 microns, 0.64cm long), 10 ml of hydrochloric acid, 5 ml of ammonium hydroxide, anddeionized water.

[0079] The silica fibers were washed in accordance with the procedure ofExample 2. The aluminaborosilicate fibers were dispersed in a 7,570 mlV-blender with 3000 grams of deionized water for 5 minutes. The washedsilica fibers, dispersed aluminaborosilicate fibers, and ammoniumhydroxide were mixed, with enough deionized water to bring the totalweight to 9,000 grams, in a 28.31 liter V-blender for 10 minutes withthe intensifier bar running. The slurry was removed from the V-blender,degassed, molded and the resulting billet fired as in Example 2. Thebillet was then transferred to the firing furnace. The furnacetemperature was increased at a rate of 220° C. per hour to the firingtemperature, 1260° C., where it was held for 5 hours. After firing, thetemperature was decreased at a rate of 220° C. per hour to 980° C., atwhich point the furnace was turned off and allowed to cool at roomtemperature. The billet was machined to 17 cm×17 cm×7.5 cm in accordancewith usual machining practices.

EXAMPLE 5

[0080] An acceptable 17 cm×17 cm×7.5 cm billet of material with yetgreater stability toward devitrification than the material produced inexample 1, having a density of 0.32 g/cc, and opacified with siliconcarbide was produced using 825 grams of silica fibers, 175 gramsaluminaborosilicate fibers (average diameter—11 microns, 0.64 cm long),35 grams of 1200 grit silicon carbide, 10 ml of hydrochloric acid, 5 mlof ammonium hydroxide, 56.8 grams of boron oxide, and deionized water.

[0081] The silica fibers were washed in accordance with the procedure ofExample 2. The boron oxide was dissolved in 4,000 grams of deionizedwater (concentration—1.42% boron oxide). The aluminaborosilicate fiberswere placed in a stainless steel basket and dipped into the boron oxidesolution (the aluminaborosilicate fibers absorbed 7 times their ownweight of the boron oxide solution). The fibers with absorbed boronoxide were then dried at 104° C. for 4 hours and calcined at 1100° C.for 1 hour. The “borated” fibers were then placed in a 7,570 ml capacitystainless steel V-blender with 5,000 grams of deionized water and mixedusing the intensifier bar for 2½ minutes to disperse the fiber. Thewashed silica fibers, dispersed “borated” aluminaborosilicate fibers,silicon carbide, and ammonium hydroxide were mixed with enough deionizedwater to bring the total weight to 15,000 grams, in a one cubic footV-blender for 20 minutes with the intensifier bar running. The slurrywas removed from the V-blender, degassed, molded, dried, fired, andmachined, as in Example 1.

EXAMPLE 6

[0082] An acceptable 17 cm×17 cm×7.5 cm billet of material with gradedproperties, having a density of 0.32 g/cc, and opacified with siliconcarbide, was produced using 825 grams of silica fibers, 175 grams ofaluminaborosilicate fibers (average diameter—11 microns, 0.64 cm long),35 grams of 1200 grit silicon carbide, 10 ml of hydrochloric acid, 5 mlof ammonium hydroxide, and deionized water.

[0083] The silica fibers were washed in accordance with the procedure ofExample 2. The aluminaborosilicate fibers were dispersed in a 7,570 mlV-blender with 5000 grams of deionized water for 5 minutes. The washedsilica fibers, dispersed aluminaborosilicate fibers, silicon carbide andammonium hydroxide were mixed with enough deionized water to bring thetotal weight to 25,000 grams, in a 28.31 liter V-blender for 15 minuteswith the intensifier bar running. The slurry was removed from theV-blender, degassed, molded, dried, fired and machined in accordancewith the procedure of Example 1.

[0084] The resulting billet of material is relatively richer in silicaat the top and aluminaborosilicate at the bottom.

EXAMPLE 7

[0085] A 17.5 cm×17.5 cm×9 cm material with a temperature capabilitygreater than that of the material of Example 1, having a density of 0.24g/cc, and opacified with silicon carbide, was produced using 750 gramsof aluminaborosilicate fibers (diameter—1 to 3 microns), 250 grams ofsilica fibers, 35 grams of silicon carbide, 5 ml of ammonium hydroxide,and deionized water. The silica fibers were dispersed in a 7,570 mlV-blender with 5,000 grams of deionized water for 5 minutes.

[0086] The dispersed silica fibers, aluminaborosilicate fibers, siliconcarbide, and ammonium hydroxide were mixed with enough deionized waterto bring the total weight to 18,000 grams, in a 28.31 liter V-blenderfor 7 minutes with the intensifier bar running. The slurry was removedfrom the V-blender, degassed, molded, and dried as in Example 2. In thefurnace, the temperature was increased at a rate of 220° C. per hour tothe firing temperature of 1370° C. where it was held for 1½ hours. Afterfiring, the temperature was decreased at a rate of 220° C. per hour to980° C., at which point the furnace was turned off and allowed to coolto room temperature. The billet was machined to 17.5 cm×17.5 cm×9 cm inaccordance with the usual machining practices.

[0087] The preferred alumina fibers are 95.2% pure and are availablefrom ICI Americas, Inc. and marketed as SAFFRIL™. The preferred diameterfor the alumina fibers ranges from 1 to about 15 microns. The preferredsilica fibers are 99.7% pure and are available from Schuller (JohnsManville Corp.), Denver, Colo. and marketed as MICROQUARTZ 108™ fibersor as Q-FIBER™. These fibers have an average diameter of 1.7 microns.However, silica fibers having diameters ranging from 1 to 6 microns areuseful in the present invention.

[0088] Also, mixtures of the above-described fibers can be used withother fibers known in the art, e.g., zirconium fibers. In addition,metal fibers and carbon fibers can be utilized by themselves or incombination with other fibers. As stated, the product of the method ofthe present invention to make the filler/reinforcer of the presentinvention may comprise as much or greater than 99% silica.

[0089] While boron nitride is considered to be the preferred boronsource, it is believed that SiB_(x), B₄C, B₂O₃, and B and other boronsources can also be used. It is preferred that boron be present in anamount from about 0.4% to about 3% by weight. Boron nitride is believedto be preferred because it is believed, due to its stability, that itpermits a more uniform fusion to fiber junction and yields superiorbonding and uniform porosity.

[0090] In addition, aluminaborosilicate fibers may be used and areavailable from 3M Company marketed under the tradename AB-312 ™ whichcontains 62% (plus/minus 2.0%) Al₂O₃, 14% (plus/minus 2.0%) B₂O₃ and 24%(plus/minus 2.0%) SiO₂. These fibers are available and useful in thepresent invention in diameters ranging from 3 to 12 microns.

[0091] The preferred composition comprised of: 21% by weight aluminafiber; 74% by weight silica fiber; 2% by weight (600 grit) siliconcarbide; and 2.85% by weight boron nitride is also availablecommercially in densities to 3 to 64 lbs./ft.³ (plus/minus ¾ lb.) fromLockheed Missiles and Space Company, Inc., Sunnyvale Calif. (“Lockheed”)under the trade name “HTP” (High Temperature Performance). For example,Lockheed commercially sells “HTP-12-22” (12 lb./ft.³ densitysilica/alumina fiber ratio of 78/22), “HTP-12-35” (12 lb./ft.³ densityin a silica/alumina fiber ratio of 65/35) and “HTP-12-45” (12 lb./ft.³density in silica/alumina fiber ratio of 55/45.

[0092] Materials Evolution & Development USA, Inc. manufactures theabove types of Ultra-low density fused fibrous ceramics under the tradename P.R.I.M.M.™ (Polymeric Rigid Inorganic Matrix Material). MaterialsEvolution & Development USA, Inc. manufacturers P.R.I.M.M.™ in densitiesvarying from 4 lb./ft.³ to 64 lb./ft.³. P.R.I.M.M.™ material is groundby mortar and pestle, or other grinding mechanism, then sieved intodifferent particulate sizes. An optimum sieved particulate size forP.R.I.M.M.™ material (16 lb/ft³ density) is approximately 180 microns indiameter. However, optimum particle sizes are believed to be dependentupon the particular application and P.R.I.M.M.™ material density, andcan range from about 10 microns to about 1000 microns. The preferredparticle size of the fused fibrous compound component of the PRIMM™product of the present invention ranges from about 180 microns to about250 microns. In addition, in some applications it may be preferable toutilize particles of a smaller size in combination with the aboveparticle size range.

[0093] The present invention includes the use of radiopacifiersincluding, but not limited to, barium sulfate, TPB, bismuth, aluminumcompounds, metal oxides, and organo-metallic compounds.

[0094] The present invention may be utilized with a variety of bonecement systems including, but not limited to, self-activating, lightcurable, heat curable, self-curing and microwave curing systems.

[0095] The density of the PRIMM™ product, i.e., the fused fibrouscompound material of the present invention ranges from about 6 lb/ft³ toabout 50 lb/ft³, preferably from about 6 lb/ft³ to about 25 lb/ft³, andmost preferably from about 6 lb/ft³ to about 16 lb/ft³.

[0096] The porosity of the PRIMM™ product, i.e., the fused fibrouscompound material of the present invention ranges from about 60% byvolume void space and up, preferably the product porosity ranges fromabout 70% by volume void space and up, and most preferably, the porosityof the fused fibrous compound of the present invention ranges from about80% by volume void space. For example, 16 lb/ft³ PRIMM™ product of thepresent invention manufactured utilizing the examples of the presentinvention comprises approximately 88% by volume void space. Set forth inFIG. 1, the relationship between density and porosity is charted.

[0097] The fused fibrous compound of the present invention (PRIMM™product) preferably has average or mean pore diameters of greater than10 microns, more preferably over 20 microns.

[0098] It is also believed that the addition of a silanation agent isbeneficial. The preferred procedure of silanation of fibers is asfollows: (1) mix 2 ml silane (Union Carbide A-174) with 2 mln-propylamine with 196 ml of cyclohexane for 15 minutes; (2) treatfibers for 2 hours in the above prepared solution and stir at roomtemperature; (3) rinse once with cyclohexane; (4) dry in air at roomtemperature for 1 hour; and (5) dry at 60° C. for 1 hour. Preferably,the fibers are silanated greater than 90% of the surface area of thefibers.

[0099] In addition, it has been found that it may be preferable whenadding the fused fibrous compound of the present invention to bonecement systems, to do so under vacuum pressure.

[0100] Flexural Testing Of Bone Cement With Fused Fibrous Compounds

[0101] Four sample groups were tested: Control 0% by weight, 10% byweight, 15% by weight, 20% by weight fused fibrous compound. Each groupcomprised 15 samples with sample dimensions of 2 mm×5 mm×20 mm. Thesamples were cured in dental stone processing flasks made of resinimpregnated gypsum rock. Impressions were made in the flasks to thesample dimensions. The flasks were then coated with a thin layer ofalcote to facilitate separation of the bone cement samples after cure.The PMMA was mixed with the fused fibrous compound and then monomerliquid added. The samples were hand-mixed for approx. 2 minutes andplaced in a mold. The flasks were pressurized under 3000 lb. for about 5minutes then clamped in place for 5 more minutes. The samples were curedunder 2 bar pressure at 45° C. for 15 minutes and then cooled for 30minutes in lukewarm water. The samples were pried out of the flasks andplaced in bags with water and stored for 2 weeks. The samples were eachsanded with 320 grit sand paper to the final dimensions prior tomechanical testing. The flexural 3 point bend tests were made onInstrom® machine. The results are summarized below in FIGS. 2 and 3.Shrinkage Testing On Bone Cement With Fused Fibrous Compounds Added TestGroups: 1 gram PMMA Control 0% fused fibrous compound (PRIMM™); 1 gramPMMA+20%, 30%, and 40% by weight PRIMM® silanated fused fibrous compoundin particle form, approximately 180-250 microns. Each group contained 1gram cement powder, 1 gram liquid monomer and 0, 0.2 grams, 0.3 grams,0.4 grams of 16 lb./ft. density fused fibrous compound. The percent byweight of fused fibrous compound is based on cement powder componentweight and not final bone cement weight. The PMMA and PRIM were placedon a glass plate and the liquid monomer was added. The samples weremixed for approximately 2.5 minutes then approximately 0.2 grams placedin a ACTA linometer. Shrinkage was recorded for 20-30 minutes persample. The results are summarized in FIG. 4, wherein the amount ofPRIMM™ brand fused fibrous compound is based on total weight ofcomposition.

[0102] The practice of the present invention also reduces thepolymerization reaction temperature of PMMA, while as recognized bythose skilled in the art, is beneficial and is shown in FIG. 5. A studywas conducted to determine the effect of PRIMM™ augmentation onpoly(methyl methacrylate) bone cement. The cement was Simplex P(Howmedica), mixed according to instructions which dictated a ratio of 2grams of powder to 2 ml of liquid. The PRIMM™ material was comprised ofsilanated 180-250 micron particles at 16 lb/ft³ density. Ten sampleswere tested by recording the core temperatures with a type Kthermocoupler probe. The samples were made by first mixing the cementpowder with the PRIMM™ and then mixing in the liquid monomer. The mixingwas performed on a glass plate with a plastic spatula for 3-4 minutesuntil the cement could be molded with gloved hands. The cement was thenpressed into a 5 ml glass flask to form a cylindrical sample with a 18mm diameter and 18-20 mm height. The probe was then inserted all the waythrough the sample. Both the glass flask and probe tip were coated witha lithium grease to encourage extraction from the cement. Temperaturerecording began at 5 minutes after initial mixing and continued until 15or 20 minutes.

[0103] While the invention has been illustrated and described in detailin the foregoing description, the same is to be considered asillustrative and not restrictive of character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. A bone or dental cement composition comprising: a bone or dental cement; and Polymeric Rigid Inorganic Material Matrix.
 2. The composition of claim 1, wherein the bone or dental cement further comprises polymethacrylate.
 3. The composition of claim 1, wherein the bone or dental cement further comprises methylmethacrylate-styrene.
 4. The composition of claim 1, wherein the bone or dental cement further comprises a radiopacifier.
 5. The composition of claim 1, wherein the composition comprises at least 10% by weight Polymeric Rigid Inorganic Material Matrix.
 6. The composition of claim 1, wherein the composition comprises at least 20% by weight Polymeric Rigid Inorganic Material Matrix.
 7. The composition of claim 1, wherein the Polymeric Rigid Inorganic Material Matrix is added in the form of particles.
 8. The composition of claim 1, wherein the Polymeric Rigid Inorganic Material Matrix has a density of between approximately 4 and 64 lb/ft³.
 9. A method for improving a bone or dental cement composition comprising adding Polymeric Rigid Inorganic Matrix Material to a bone or dental cement composition.
 10. The method of claim 9, wherein the Polymeric Rigid Inorganic Matrix Material is added in the form of particles.
 11. The method of claim 9, wherein the Polymeric Rigid Inorganic Matrix Material has a density of between approximately 4 and 64 lb/ft³.
 12. The method of claim 9, further comprising adding at least 10% by weight Polymeric Rigid Inorganic Material Matrix.
 13. The method of claim 9, further comprising adding at least 20% by weight Polymeric Rigid Inorganic Material Matrix.
 14. A bone or dental cement treatment kit for bone or tooth repair or other treatment of a bone or tooth defect, the kit comprising: a finely divided acrylic polymer; polymerizable liquid acrylate monomers for preparation of bone or dental cement useful in bone or tooth repair or other bone or tooth treatment; and Polymeric Rigid Inorganic Matrix Material.
 15. The kit of claim 14, wherein the polymer comprises polymethylmethacrylate.
 16. The kit of claim 14, wherein the acrylic monomers comprise methylmethacrylate-styrene-copolymer.
 17. The kit of claim 14, further comprising a radiopacifier.
 18. The kit of claim 14, wherein the Polymeric Rigid Inorganic Matrix Material is provided in the form of particles.
 19. The kit of claim 14, wherein the Polymeric Rigid Inorganic Matrix Material has a density of between approximately 4 and 64 lb/ft³. 